Regulation of carbonic anhydrase expression by zinc, cobalt, and carbon dioxide in the marine diatom Thalassiosira weissflogii

TWCA1 is the major Zn-requiring isoform of carbonic anhydrase (CA) in the m arine diatom Thalassiosira weissflogii. We have examined the roles that tra ce metals and CO, play in the regulation of TWCA1 expression over ranges of concentrations that bracket those encountered in the marine environment. B oth steady-state levels of TWCA1 and the kinetics of induction were measure d by western analysis. TWCA1 levels correlated well with cellular CA activi ty levels. TWCA1 was induced at a low CO2 concentration but the level of in duction, as determined by western analysis, was dependent on the availabili ty of Zn. Co effectively substituted for Zn in regulating TWCA1 expression and promoting TWCA1 activity. Upon shift from low to high CO2, the concentr ation of TWCA1 decreased. The expression of TWCA1 is diel cycle regulated, and cellular TWCA1 decreased during the dark phase. These results provide t he basis for studying the expression of CA in field populations and, taken together with previous radiolabeling studies, provide strong evidence of in vivo metal substitution of Co for Zn in a CA. Our data also support the co nclusion that TWCA1 plays a central role in carbon acquisition in T. weissf logii.